1. Technical Field
The technical field relates to a chip structure, and more particularly, to a chip structure having a bonding wire.
2. Background
Due to crisis of oil depletion, vehicle energy-saving technology is the most important goal of in current stage of human civilization development. As human populations become concentrated of in cities, people's daily commuting time has gradually increased, and aging of the population has led to prolonged journey time; and therefore, personal electric vehicles focused on vehicular space, safety and energy-saving have been gradually developed, and industries and research institutions have been actively involved in developments of related technologies.
Wire bonding is one of the key technologies in a vehicle power module. During the past, the wire bonding of the vehicle power module is typically performed with an aluminum bonding wire, but with recent sharp increase in the power of the vehicle power module, the industries have gradually tried to replace the aluminum bonding wire with a copper bonding wire, which has a higher melting point and more favorable conductivity. However, an interface between the copper bonding wire and an aluminum bonding pad on a chip is prone to produce intermediate metallic compounds due to a chemical reaction under a high temperature working environment of the high-power vehicle power module, and this chemical reaction can lead a plurality of holes being generated between the copper bonding wire and the aluminum bonding pad, thereby damaging a bonding strength therebetween. In addition, a hardness of the copper bonding wire is higher than a hardness of the aluminum bonding pad, such that the cooper bonding wire is less susceptible to deformation during the wire bonding process, and thus the bonding force during the wire bonding is required to be increased, so that the copper bonding wire can be adequately deformed to attain a favorable bonding strength. Nevertheless, the aforementioned approach might lead to a greater stress concentration and thereby damage the aluminum bonding pad with lower hardness or cause damages to the chip underneath the aluminum bonding pad.